Estimating kinetic mechanisms with prior knowledge. A model can be made to fit experimental data while also satisfying user-defined constraints that establish explicit relationships between model parameters or that define specific model behaviors. In the absence of constraints, a fitting algorithm will search a potentially large parameter space to find a solution that best explains the data. Adding constraints to the model not only enforces prior knowledge but also accelerates the fitting procedure by narrowing the search space and reducing the number of free parameters. Furthermore, constraints can be used as a mechanism for testing hypotheses against experimental data.